Color picture tube with deflection center control

ABSTRACT

A color picture tube consisting of a shadow mask, color prosphors, a deflection yoke and a magnetic compensating alloy ring provided adjacent to the deflection yoke for changing a magnetic flux therethrough in response to the temperature on the shadow mask.

United States Patent [191 Ohgoshi et a1. 0

COLOR PICTURE TUBE WITH DEFLECTION CENTER CONTROL Inventors: Akio Ohgoshi; Yoshiharu Katagiri,

both of Tokyo, Japan Assignee: Sony Corporation, Tokyo, Japan Filed: Sept. 30, 1969 App]. No.: 862,411

Foreign Application Priority Data Oct. 8, 1968 Japan 73723/68 US. Cl. 313/75, 335/217 rm. C1 H01j 29/56, H01 j 29/76' Field of Search 313/75, 79; 335/217 References Cited UNITED STATES PATENTS 2/1966 Schubert 313/84 Primary Examiner-Robert Segal Attorney, Agent, or Fir mLewis H. Eslinger, Esq.; Alvin Sinderbrand, Esq.

[57] ABSTRACT A color picture tube consisting of a shadow mask, color prosphors, a deflection yoke and a magnetic compensating alloy ring provided adjacent to the deflection yoke for changing a magnetic flux therethrough in response to the temperature on the shadow mask. v

6 Claims, 12 Drawing Figures SHEET NF 4 I N VEN TOR.

AKIO OHGOSl-II YOSHIHARU KATAGIRI ATTORNEYS SIEET 2 0F 4 PATENIEUwszomm a m m Q 0 0 w 0 bcfi INVENTOR. AKIO OHGOSHI YOSHIHARU KATAGIRI ATTORNEYS PATENTEBMJEZOIQM l N VEN TOR.

OHGOSHI ARU KATAGIRI A l TOR N15 YS PAIENTED 3.831 .051

W t N 4 1 N VEN TOR.

AKIO OHGOSHI YOSHIHARU KATAGIRI 1; y Y ATTORNEYS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a color picture tube, and more particularly to a system of compensation for mislanding of an electron beam resulting from the temperature variation in the color picture tube.

2. Description of the Prior Art Generally, a color picture tube has incorporated in its envelope the so-called shadow mask or a grid apparatus made up of many metal strips so as to ensure impingement of a plurality of electron beams on predetermined color phosphors. During picture reception electrons of the beams strike against the shadow mask or the grid apparatus to heat it, so that the shadow mask or the grid apparatus is subjected to thermal expansion to be deformed. This leads to changes in the spacing between apertures of the shadow mask or slits of the grid apparatus, which causesthe electronbeams notto impinge on the predetermined phosphors to introduce the socalled mislanding of the electron beams.

To avoid this, it has been the practice in the art to provide at a mechanical holding portion of the-shadow mask or the grid apparatus a holder unit which is deformed in response to temperature, by means of which the shadow mask or grid apparatus is mechanically shifted in position to change the spacing between it and the color phosphors. However, the holder unit is complicated in construction and its support is uncertain, so that a difficulty is encountered in the holding of the holder unit when subjected to shock conditions.

SUMMARY OF THE INVENTION netic member is formed of an iron-nickel, nickelcopper alloy or the like which has negative magnetictemperature characteristics and is commonly-referred to as a magnetic compensating alloy. According to our experiments, it has been found that the rate of temperature rise to time at the shadow mask or grid apparatus is substantially the same as those at the funnel and neck portions of the color picture tube and at a position where the deflection yoke is disposed. Consequently, the aforementioned magnetic compen sating alloy member need not always be located in the proximity of the shadow mask or the grid apparatus and the provision of such an alloy member at the abovementioned place enables the compensation of mislanding of electron beams. 1

Accordingly, one object of this invention is to provide a color picture tube which is adapted to compensate for mislanding of electron beams without the use of mechanical means.

Another object of this invention is to provide a color picture tube which is designed to move the deflection center in accordance with the degree of mislanding of electron beams resulting from thermal expansion of a shadow mask.

Still another object of this invention is to provide a color picture tube in which the magnetic flux distribution over the deflection yoke is caused to vary with temperature by the use of a magnetic compensating alloy member so as to avoid color contamination due to mislanding of electron beams.

Other objects, features and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view schematically illustrating a color picture tube for explaining the present invention;

FIG. 2 is a cross-sectional view of the principal portion of a color picture tube, illustrating one example of this invention;

FIG. 3 is a graph showing the temperature-permeability characteristic of a magnetic compensating alloy usable in this invention;

FIGS. 4A, 4B and 5A, 5B are respectively schematic plan and cross-sectional views for explaining the operational principles of this invention;

' FIGS. 6A and 6B are respectively plan and crosssectional views of the principal portion of a color picture tube, illustrating another example of this invention;

, FIG. 7A is a perspective view showing one example of a ring-shaped magnetic compensating alloy member that may be used in accordance with the invention, and FIG. 7B is a similar view showing the ring-shaped magnetic compensating alloy member employed in the color picture tube of FIGS. 6A and 6B; and

FIG. 8 is a schematic perspective view of another example of the ring-shaped magnetic compensating alloy member as applied to an electron gun device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic cross-sectional view of a color picture tube, for explaining mislanding of an electron beam which is caused by deformation of a mask due to interior surface of a color picture tube 1, is heated by the impingement of an'electron beam to be thermally expanded as indicated by 3' (shown on the inside of the normal position for convenience of illustration), the deformation of the mask 3 causes displacement of the apertures 4 of the mask as indicated by 4 to introduce mislanding of the electron beam. This displacement of the apertures 4 becomes greater as the periphery of the mask 3 is approached from the center thereof. For example, the central point of an aperture 3a shifts from A to A' as shown. Accordingly, an electron beam 5, which would be deflected from the deflection center 0 of a deflection yoke 6 to pass the center A of, for example, the aperture 3a and impinge upon the phosphor screen 2 at a predetermined position P during normal mask at such positions as to permit the passage therethrough of the electron beam for its correct landing on the screen. However, such a mechanical movement of the mask necessitates the use of a complicated support for supporting the mask to the panel portion at a predetermined position and is likely to introduce uncertainty in the supporting of the mask, so that the shock resistance of the mask is not great when subjected to shock conditions.

Assuming that the deflection center 0 of the electron beam is shifted rearwardly in FIG. 1, the incident angle of the beam to an aperture 3a is smaller than that obtainable with the deflection center 0 at its initial position. Accordingly, even if the electron beam deflection center 0 is shifted rearwardly on the line X-X to a position O" spaced from its initial position by a predetermined distance L, the electron beam passing through the aperture 3a' is impinged upon the phosphor screen 2 at the normal position P. Thus, the mislanding of the electron beam can be compensated for.

In view of; the foregoing, the present invention is to detect a temperature change of a portion at which temperature varies in substantially the same manner as that of the mask and to locate the deflection center of the deflection yoke in accordance with the detected temperature change so as to avoid the mislanding of the electron beam.

In the case of using a mask such as a shadow mask having many apertures, the compensation of the mislanding is required for both horizontal and vertical deflections but in the case of using a mask such as a grid apparatus having slits the compensation is necessary only for horizontal deflection.

Referring now to FIG. 2, one concrete embodiment of this invention will hereinbelow be described in detail, in which similar elements to those in FIG. 1 are identified by the similar reference numerals and will not be described for the sake of brevity.

According to our experiments, it has been found that the temperature rise at the funnel and neck of the picture tube and the portion where the deflection center is located is substantially equal to that of the mask. In the present invention, as shown in FIG. 2, there is mounted on the rear end portion of the deflection yoke 6 a ring-shaped magnetic compensating alloy member 7 of a high negative temperature coefficient to magnetism, that is, the permeability of which member appreciably decreases with an increase in temperature. The ring-shaped magnetic compensating alloy member 7 may be formed of an alloy composed of, for example, 70 percent of iron and 30 percent of nickel, and one example of its temperature-permeability characteristic is as shown in FIG. 3 in which the abscissa represents temperature and the ordinate permeability.

It appears from the graph that the permeability of the ringshaped magnetic compensating alloy member 7 is high when its temperature is low and that the permeability gradually decreases with an increase in the temperature. With the ring-shaped magnetic compensating alloy member 7 mounted on the rear end portion of the deflection yoke 6 as depicted in FIG. 2, when the temperature at the deflection yoke mounting portion of the picture tube is low and consequently the temperature of the alloy member 7 is low, its permeability is high with result that one portion of the magnetic flux 8 at the rear end portion of the deflection yoke by-passes the alloy member 7 as shown in FIG. 4, thereby to cause a substantial decrease in the magnetic flux 8 passing through the neck at the rear end portion of the deflection yoke 6. Namely, the magnetic compensating alloy member 7 decreases the magnetic flux 8'for deflecting the electron beam at that particular portion, by which the deflection center 0 of the deflection yoke is shifted forwardly to a position indicated by 0'. Without the alloy member 7, the deflection center stays at the position 0. When the temperature of the deflection center mounting portion rises to increase the temperature of the ring-shaped magnetic compensating alloy member 7, its permeability decreases to cause an increase in the reluctance of the alloy member 7, by which the magnetic flux flowing in the alloy member 7 is decreased, thus causing an increase inthe magnetic flux 8 at therear end portion of thedeflection yoke 6, as illustrated in FIG. 5. With the increase of the magnetic flux 8, the deflection center 0 is. shifted rearwardly to a position 0''. I

In this case, the amount of increase or decreasein the magnetic flux caused by the temperature variation is in proportion to the cross-sectional area of the. ring shaped magnetic compensating alloy member 7, so that a suitabl'ejselection of the cross-sectional area of the alloy member 7 leads to the selection of the amount of displacement of the deflection center at a predetermined value. Although the present example has been described in connection with a'magnetic field in one direction, the ring-shaped magnetic compensating.

7 is mounted on the picture tube in a manner to position the deflection center at its normal location under normal temperature conditions. In such a case, when the mask is thermally expanded with its temperature rise the deflection center of the deflection yoke is shifted rearwardly in accordance with the temperature rise to compensate for mislanding of the beam.

Referring now to FIGS. 6A, 68, 7A and 7B, the ringshaped magnetic compensating alloy member 7 will hereinbelow be discussed concretely. In practice, it is preferred that a metal fitting for fixedly mounting the deflection yoke 6 about the picture tube 1 as depicted in FIG. 6 is formed of a magnetic compensating alloy. Namely, such a metal fitting is used as the ring-shaped magnetic compensating alloy member 7 described above. The metal fitting, indicated by 7 in the figures, may be simply a ring-shaped strap such as shown in FIG. 7A in which both ends are bent and clamped, for example, by means of a bolt 9. Alternatively, the metal fitting 7 may be in the form depicted in FIGS. 6A, 6B and 7B in which it consists of two semicircular members and they are assembled together in the form of a ring and are clamped at their ends by bolts. In this case, the metal fitting, that is, the ring-shaped magnetic compensating alloy member 7 is mounted onthe picture tube 1 in such a manner that its gap or gaps 9 may lie in parallel relation to the line 2-2 in FIG. 6A for the reason that one portion of the horizontal deflection magnetic field is equally by-passed on both sides of the ring-shaped magnetic compensating alloy member 7. In FIG 6 reference numeral 10 designates a horizontal winding and 11 a cover of the deflection yoke 6.

The ring-shaped magnetic compensating alloy member 7 need not always be disposed on the outside of the picture tube 1 but it may be placed within the tube 1 in the vicinity of the rear end portion of the deflection yoke. Namely, the alloy member 7 may be mounted on the top end portion of an electron gun devicel2 at a position corresponding to the rear end portion of the deflection yoke as depicted in FIG. 8. FIG. 8 shows one example of this invention as applied to the electron gun device 12 of such single-gun, plural-beam type construction as disclosed in, for example, the U.S. Pat. No. 3,448,316. Reference numeral 13 indicates an electron gun, and 14 deflecting plates by means of which electron beams passing through a main electron lens formed by third, fourth and fifth grids of the electron gun l3 and crossing each other are deflected in predetermined directions. Reference numeral 15 designates bead for holding the deflecting plates 14 and 16 a getter ring. In the illustrated example the ring-shaped magnetic compensating alloy member 7 is disposed around, the deflecting plates 14 and the same results as the above-described can be obtained, even if the deflecting plates 14 are formed of a magnetic compensating alloy.

It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of this invention.

We claim as our invention:

1. A color picture tube comprising an envelope having a face plate, a screen of different phosphors coated on said face plate for emitting light of respective predetermined colors, an electron gun device for generating at least one electron beam directed toward said face plate for impingement on said screen, a beam selecting means disposed adjacent said face plate and having apertures through which said beam can pass to. land on selected phosphors of said screen in accordance with the angle of incidence of said beam to said beam selecting means at the apertures of the latter, magnetic deflection means fixed on said envelope and operative to produce magnetic flux for deflecting said beam from a deflector center within said deflection means so as to cause scanning of said screen by said beam, and a magnetic flux shunting member also fixedly located with respectto said envelope and being disposed adjacent said magnetic deflection means at an axial distance from said deflection center for shunting a portion of said magnetic flux produced by said magnetic deflection means, said flux shunting member having a magnetic permeability that varies with changes in the temperature thereof for varying said portion of the flux which is shunted and axially shifting said deflection center, thereby to compensate for thermal expansion of said beam selecting means.

2. A color picture tube according to claim 1, in which said magnetic flux shunting member is'in the form of a ring disposed at the side of said magnetic deflection means remote from said screen and said permeability decreases in accordance with increasing temperature,

whereby substantial magnetic flux from said side of the magnetic deflection means is shunted through said member at low temperature and the magnetic flux thus shunted is decreased progressively with increasing temperature.

3. A color picture tube according to claim 1, wherein said flux shunting member also functions to mount said magnetic deflection means on said envelope.

4. A color picture tube according to claim 1, in which said flux shunting member is at the exterior of said envelope. I

5. A color picture tube according to claim 1, in which said flux shunting member is in the interior of said envelope.

6. A color picture tube according to claim 1, in which said flux shunting member is of a nickel-iron alloy containing approximately 30 percent of nickel. 

1. A color picture tube comprising an envelope having a face plate, a screen of different phosphors coated on said face plate for emitting light of respective predetermined colors, an electron gun device for generating at least one electron beam directed toward said face plate for impingement on said screen, a beam selecting means disposed adjacent said face plate and having apertures through which said beam can pass to land on selected phosphors of said screen in accordance with the angle of incidence of said beam to said beam selecting means at the apertures of the latter, magnetic deflection means fixed on said envelope and operative to produce magnetic flux for deflecting said beam from a deflector center within said deflection means so as to cause scanning of said screen by said beam, and a magnetic flux shunting member also fixedly located with respect to said envelope and being disposed adjacent said magnetic deflection means at an axial distance from said deflection center for shunting a portion of said magnetic flux produced by said magnetic deflection means, said flux shunting member having a magnetic permeability that varies with changes in the temperature thereof for varying said portion of the flux which is shunted and axially shifting said deflection center, thereby to compensate for thermal expansion of said beam selecting means.
 2. A color picture tube according to claim 1, in which said magnetic flux shunting member is in the form of a ring disposed at the side of said magnetic deflection means remote from said screen and said permeability decreases in accordance with increasing temperature, whereby substantial magnetic flux from said side of the magnetic deflection means is shunted through said member at low temperature and the magnetic flux thus shunted is decreased progressively with increasing temperature.
 3. A color picture tube according to claim 1, wherein said flux shunting member also functions to mount said magnetic deflection means on said envelope.
 4. A color picture tube according to claim 1, in which said flux shunting member is at the exterior of said envelope.
 5. A color picture tube according to claim 1, in which said flux shunting member is in the interior of said envelope.
 6. A color picture tube according to claim 1, in which said flux shunting member is of a nickel-iron alloy containing approximately 30 percent of nickel. 